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STM32L476 high current draw before programming

Associate II
Posted on January 06, 2017 at 22:16

Our application uses the SMT32L4 in a 4-20mA loop-powered transmitter. VCC on this device is 3V. The typical current draw once the product is operational is approximately 8mA @ 3v. We are utilizing the bootloader to program the mcu with UART1 on pins 68-69 (PA9 and PA10). On some boards, prior to programming, there is approximately 40-50mA current draw on the 3V supply. Our supply is rated for 50mA and once we attempt to initiate bootloading, the current consumption increases beyond that limit. If we provide enough current by increasing the supply, the device programs successfully. Once programmed, the total draw on the 3V supply is the expected 8mA.

I am wondering if there is a known operation/current consumption for these devices before they are initially programmed. Also, I see that the bootloader can use USART1/2/3, I2C1/2/3, and DFU (USB). Which ports/pins are utilized for the USART and I2C channels during bootloader operation? There are several ports that can be configured for each of these channels during normal operation, so it is difficult to determine the exact pin configuration of the device when it is in bootloader mode.

Thank you!


#programming #high-current #bootloader #stm32
Posted on January 12, 2017 at 20:09


I can't then think of nothing but to carefully cut one pin after another to find the culprit.

You can try to do it the other way round - get a 'L4 Nucleo (or Disco, but there are several external parts on that) and try the boot process there, while measuring the current consumption. Then gradually add connections similar to your board.


Posted on January 12, 2017 at 23:53

For current measurements I often start with a bare board, solder on the micro and a few capacitors. For Boot0 the only thing I have connected to it is a weak pull-down and pull it high with a simple slide switch (production applications I pull it high (external to the PCB) with a spring loaded test probe - so for programming all I need is a jig with spring loaded test probes for GND, VCC, TX, RX, BOOT0, RESET contacts on the PCB)

Associate II
Posted on January 30, 2017 at 04:31

Buy a NUCLEO-L476RG board for $15 and see if the problem exists there for some more clues.